The formation of formic acid by the hydrolysis of alkyl formates is well-known in the art. The major drawback of such processes from the commercial standpoint is that the chemical equilibrium of the hydrolysis reaction does not favor the rapid formation of substantial amounts of formic acid. Even with mineral acid catalyst and high temperatures, the extended residence time necessary to reach equilibrium makes the process very complicated and expensive. Examples of such processes are shown in U.S. Pat. No. 2,160,064 and British Pat. No. 628,656. Though the use of the mineral acid catalyst did reduce reaction time, it created problems because of its tendency to promote the decomposition of the formic acid to carbon monoxide and water.
In recent years, the trend has been to perform the hydrolysis by using formic acid itself as the catalyst. While this overcame certain of the decomposition problems caused by the use of a strong mineral acid, the formic acid is less effective in accelerating the reaction.
To overcome this problem, U.S. Pat. No. 3,907,884 proposed the use of a solvent system to reduce the reaction equilibrium time at temperatures from 25.degree. to 150.degree. C. This process, however, while it serves to increase the reaction rate, is not fully effective because the reactants during purification tend to undergo a reverse reaction, that is, the formic acid and the methyl alcohol present in high concentrations and at high temperatures reesterified to reform substantial quantities to the methyl formate.
Another deficiency with the process taught in U.S. Pat. No. 3,907,884 is that it proposes adding the formic acid catalyst from an extraneous source. Obviously, this procedure results in decreasing the net production of formic acid and effectively reducing the capacity of the equipment.